Extinguishant for metal fires

ABSTRACT

Carbon microspheres are used as an extinguishant for metal fires.

1 United States Patent 1191 Schmitt Oct. 8, 1974 EXTINGUISHANT FOR METALFIRES 2,385,500 9/1945 Fasold 252/2 3,090,749 5 1963 W k 252 2 [75]Inventor: Charles Schmm Oak Rldge, 3,475,332 10/1969 M12311 al 252/2Tenn- 3,544,459 12/1970 111m 252/2 [73] Assignee: The United States ofAmerica as represented by the United States Atomic Energy Commission,Primary -L y K1118 Washington, DC Attorney, Agent, or Firm-John A.Horan; David S. Zachry; John B. Hardaway [22] Filed: May 3, 1973 [21]App]. N0.: 356,865

52 us. (:1. 169/43, 252/2 [57] ABSTRACT [51] Int. Cl. A62c 3/00 [58]Field of Search 252/2; 169/1 R, 2 R Carbon mlcfospheres are used as anextmgulshant for metal fires. [56]. References Cited UNITED STATESPATENTS 4 Claims, No Drawings 2,346,627 4/1944 Thrune 252/2 BACKGROUNDOF THE INVENTION This invention was made in the course of, or under, acontract with the United States Atomic Energy Commission. It relatesgenerally to a method for extinguishing metal fires.

Pyrophoric metals present a hazard in many industrial areas. Basically,the pyrophoric metals include the alkali and alkaline earth metals.However, many of the rare earth and actinide metals are also pyrophoric.In nuclear processing facilities, sodium, potassium, 'uranium, thorium,and zirconium are the metals which present the principal hazards.

Many solid extinquishants are commercially available for extinguishingmetal fires. However, not all extinguishants are suitable for all metalfires and others have detrimental side effects. Silica is satisfactoryfor extinguishing some fires. However, when silica is placed on aburning sodium potassium mixture, it actually reacts with the burningmetal to produce a larger fire. Graphite flour and flakes have proven tobe an effective means of extinguishing a metal fire. However, thepresent graphite extinguishants produce great clouds of black dust whenprojected at a fire. If projected within an enclosure, such as anordinary room, the air becomes contaminated with finely divided graphiteto the extent that sight and respiration are impossible without specialequipment. Sodium chloride has also been used to effectively extinguishmetal fires. However, sodium chloride is extremely corrosive. Anyequipment in the vicinity of the fire is subject to corrosion by thesodium chloride. Phosphate extinguishants have also been used in theprior art. However, these extinguishants also have a dusting problem aswell as causing additional smoke to be emitted from the fire.

In using the above extinguishants it is conventional to use a cannisterfilled with the extinguishant and supplied with a source of pressurizedgas such as N or C The cannisters normally communicate with a hose andnozzle fitting. In use the pressurized gas forces the extinguishant outof the cannister through the hose and nozzle fitting to create acontinuous projection of extinguishant. When a solid, such as thosedescribed above, is used as the extinguishant, clogging of the hose andnozzle assembly is a frequent problem. Thisproblem is particularly acutewhen the extinguishant is a hygroscopic material. If moisture existswithin or leaks into the cannister, the hygroscopic material becomessticky so as to effectively prevent any spraying from the cannister atall.

Another problem with some solid extinguishants is that they have aspecific gravity which is greater than that of some molten pyrophoricmetals. In such cases, the extinguishant is ineffective because theextinguishant merely sinks through the molten metal so as not toseparate the metal from the surrounding-air.

SUMMARY OF THE INVENTION It is thus an object of this invention toprovide a new extinguishant for metal fires.

It is a further object of this invention to provide a solidextinguishant which can be projected like a liquid and which doesnotdust when projected at a fire.

It is a still further object of this invention to provide an essentiallyinert extinguishant for metal fires which will not increase the amountof smoke given off from the fire.

These and other objects are accomplished by using carbon microspheres asan extinguishant for metal fires.

DETAILED DESCRIPTION According to this invention it has been found thatcarbon or graphite microspheres can be used as an extinguishant formetal fires with none of the disadvantages that adhere in the prior artuse of graphite flour or flakes. Carbon microspheres can be projectedfrom a conventional powder extinguisher cannister with flow andprojection qualities that approximate those of a liquid. Since themicrospheres have liquid-like flow properties, there is generally noproblem with clogging or sticking within the extinguisher cannister.

Carbon microspheres have a mass such that when sprayed through the air,no dusting occurs. The use of the extinguishant of this invention thusmakes it possible to extinguish a fire within an enclosure withoutcreating clouds of noxious dust. By concentrating the extinguishant onlyon the fire, clean up problems after the fire are greatly reduced sincethe surrounding area is not covered with extinguishant. Carbonmicrospheres are essentially inert so that no additional smoke iscreated when the microspheres contact the burning metal. Once the fireis extinguished, the metal may be easily recovered since no actualreaction occurs between the microspheres and the metal to produceundesirable contaminants. A simple mechanical separation process may beused to separate the microspheres from the previously burning metal.

Carbon microspheres used in the process of this invention extinguishmetal fires by first covering the metal surface and thus separating themetal from an oxygen source, and secondly by conducting heat away fromthe burning metal. Since carbon is of very low density, it willnaturally float on the surface of most metals. On metals of lowerdensity, such as lithium, individual microspheresare not heavy enough tobreak the surface tension so that they are retained on the surface ofthe metal.

Microspheres for use in the process of this invention have the followingcharacteristics. The microspheres may be within a size range of 50to'250 microns in radius, but preferably within the range of about tomicrons. While it is preferred that the microspheres for use in thisinvention be as nearly spherical as possible, it has been found thatmicrospheres or microspheroids having a major to minor axis ratio of upto about 1.5 are useful in the process of this invention. Themicrospheres preferably have a bulk density within the range of 1.2 g/ccto 1.9 g/cc and a real particle density or toluene displacement densityof 1.3 g/cc to 2.0 g/cc. The internal particle porosity of themicroparticles may range from 0.5 to 10.0 percent for use in the processof this invention. Although not a critical characteristic, it has beenfound that the microparticle compressive strength should be in the rangeof from 10 to 60 ounces per particle, depending upon particle diameter,so that the particle has sufficient strength to-withstand velocityimpact forces during projection andnot be subject to excessivefracturing. Microspheres for use in the invention preferablyhave .anorganic content of less than about A higher organic content can causewater adsorption and sticking of the particles.

Microspheres for use with this invention can be prepared by coking aresin such as a cation exchange resin at a temperature of about 850 C inan atmosphere of 5 nitrogen. However, such microspheres are presentlycommercially available with a very high degree of sphericity. Atpresent, the cheapest source of a suitable microsphere for use in theprocess of this invention is fluidized petroleum coke. Fluidizedpetroleum coke having an average major to minor axis ratio of about 1.25does not possess the sphericity of coked resin beads; however, thepetroleum coke is suitable for use in the process of this invention.

A conventional powder cannister is suitable for use in this invention. Acartridge-type extinguisher as illustrated in Fire Protection Handbook,13th Edition (1969), G. H. Tyron, Editor, pages 18-36, is the preferredextinguisher. It has also been found desirable to modify this type ofextinguisher by providing a gate valve between the CO cartridge and thechamber so that the pressure buildup may be relieved in the event ofblockage.

As a test of this process of this invention, five pounds of coked resinmicrospheres formed by heating styrene divinylbenzene resin beads inflowing nitrogen over a gradual heating period of 48 hours were packedinto the extinguisher cannister described above. The carbon microsphereswere 50 to 100 mesh in size. The cannister was supplied with a C0pressure of about 20 psig.

About one pound of magnesium shavings were ignited inside an open metalcontainer. The microspheres were blown from the cannister at a distanceof 25 feet from the fire. The fire was extinguished within less than aminute. About three pounds of microspheres were used. Similar successfultests were carried out with lithium and sodium fires.

While this invention has been described in terms of carbon or graphitemicrospheres, several modifications are readily apparent to those ofordinary skill in the art. Such modifications may include impregnationof the microspheres with a neutron poison for use on uranium fires wherea danger of criticality may exist.

What is claimed is:

1. A method for extinguishing a metal fire comprising placing on saidfire an extinguishant consisting essentially of microspheroids ofcarbon, said microspheroids having a major to minor axis ratio of lessthan 1.5 and being in size substantially within the range of 50 to 250microns in radius.

2. The method according to claim 1 wherein said microspheroids have anorganic content of less than 10 percent.

3. The method according to claim 1 wherein said microspheroids have abulk density within the range of 1.2 to 1.9 grams per cubic centimeter.

4. The method according to claim 1 wherein said microspheroids areprojected onto said fire using a pressurized gas as a means ofprojection.

1. A METHOD FOR EXTINGUISHING A METAL FIRE COMPRISING PLACING ON SAIDFIRE AN EXTINGUISHANT CONSISTING ESSENTIALLY OF MICROSPHEROIDS OFCARBON, SAID MICROSPHEROIDS HAVING A MAJOR TO MINOR AXIS RATIO OF LESSTHAN 1.5 AND BEING IN SIZE SUBSTANTIALLY WITHIN THE RANGE OF 50 TO 250MICRONS IN RADIUS,
 2. The method according to claim 1 wherein saidmicrospheroids have an organic content of less than 10 percent.
 3. Themethod according to claim 1 wherein said microspheroids have a bulkdensity within the range of 1.2 to 1.9 grams per cubic centimeter. 4.The method according to claim 1 wherein said microspheroids areprojected onto said fire using a pressurized gas as a means ofprojection.